1. Field of the Invention
The invention relates to AC to DC power conversion, particularly where the DC potential is regulated.
2. Prior Art
There are countless circuits for receiving an AC potential such as a 60 Hz power source, and converting it to a regulated DC potential. Often, the DC current flow to the load is controlled to provide regulation. For instance, a transistor may be coupled in series with the load and the flow of current through this transistor is controlled to regulate the DC potential. In such circuits, the transistor consumes relatively large amounts of power and are often expensive devices. As will be seen, the present invention uses a capacitor and switch to provide regulation without substantial power consumption.
Switching power supplies employing a switching transformer are commonly used to provide a regulated DC potential for integrated circuits. Typically, the 60 Hz line potential is converted to a DC potential by a rectifier and this DC potential is switched at a much high frequency through a transformer. This switching is controlled causing a regulated potential on the secondary windings of the transformer which, after rectification, provides the regulated DC potential (e.g., 5 volts for integrated circuits). See U.S. Pat. No. 4,347,559 for one such power supply. The DC potential which is switched at the primary winding, is typically unregulated. To provide regulation of this DC potential for the switching power supply is quite expensive and not used. Transformers needed at 60 cycles for this regulation and/or isolation are large, and hence, costly. The present invention is particularly useful in a switching power supply to control the DC voltage on the primary winding of the transformer.
In the prior art there are power supplies which utilize capacitors in series with or in connection with rectifiers, but these circuits do not use the switching means of the present invention to provide regulation through the capacitor. One such prior art circuit is shown in U.S. Pat. No. 3,001,120. Other prior art circuits showing capacitors and inductors used in conjunction with rectifiers, but in a different manner than the present invention, are U.S. Pat. Nos. 3,978,388; 4,245,294; and 4,322,787. U.S. Pat. No. 3,324,378 illustrates switching in conjunction with a rectifier but no series capacitors.